A solution of organic colloids is to be concentrated from 15 to 50 percent solids in a vertical-tube evaporator. The solution has a negligible elevation in boiling point, and the specific heat of the feed is 0.93. Saturated steam is available at 0.8 atm abs, and the pressure in the condenser is 100 mm Hg abs. The feed enters at 15°C. The over-all coefficient is 1.700 W/m². °C. The evaporator must evaporate 25,000 kg of water per hour. How many square meters of surface are required, and what is the steam consumption in kilograms per hour?